The US has hit its debt ceiling. As of December 31 2012, the US Treasury says

I can confirm we will reach the statutory debt limit today, Dec. 31

It has gone up from an unimaginable $14.3 trillion in August last year to $16.394tn as part of a package agreed then. After the fiscal cliff deal, the level of the debt ceiling is the next big debate to be had.

But what is the debt ceiling? Under US law, all government borrowing has to be approved by Congress, and they do this by limiting the amount that can be borrowed: this is the debt ceiling.

The latest figures, taking into account the new raise, show that:

• The debt ceiling has been changed 104 times since 1944 - 94 increases and 10 decreases• It has been raised 54 times by Republicans, 40 times by Democrats• Ronald Reagan increased the debt ceiling by 18 times, followed by Jimmy Carter and Lyndon Johnson by 10 times and George Bush Sr by 9 times• So far, Barack Obama has raised the debt ceiling by six times - less than George W Bush's 7 times

The previous time it went up, in February 2010, the figure increased to $14.294 trillion. The debt reached that limit and was then raised by $400bn.